The present disclosure relates to a moving image encoding method, and more particularly, relates to a moving image encoding method for compression encoding a plurality of moving image signals and a moving image encoding device.
As methods for encoding a moving image signal, there have been two encoding methods. A first one is a method in which spatial redundancy in a single frame is reduced and compression is performed and is called intra encoding. A second one is a method in which temporal redundancies in a plurality of frames are reduced and compression is performed and is called inter encoding.
Intra encoding is normally performed in micro block unit. In the intra encoding, a prediction image is generated from a peripheral image of each target micro block that is to be encoded in accordance with a corresponding prediction mode, a prediction mode in which a difference is the smallest is determined, the difference is encoded to reduce spatial redundancy. Therefore, as the number of types of prediction modes increases, the amount of processing increases.
Inter encoding is normally performed in macro block unit. In the inter encoding, block matching between a target macro block that is to be encoded and a reference image formed of an image separated from the target macro block by one field or more is performed for each micro block, a macro block with a small difference is searched, the difference is encoded, and temporal redundancy is reduced. A great number of arithmetic processings are required for this search.
Thus, a correct prediction image can be achieved by precisely generating a prediction image, thereby improving image quality. However, whether the intra encoding or the inter encoding is performed, a large arithmetic processing amount is required.
Also, there are an increasing number of applications that require simultaneous compression of a plurality of moving images. When a plurality of moving image signals are handled, the above-described processings have to be simultaneously performed on the moving image signals. Thus, the processing amount of prediction processing increases in accordance with the number of moving image signals to be handled. In the worst case, prediction processing cannot be performed in time and, disadvantageously, a prediction image might not be produced.
In order to avoid the above-described case, when a plurality of moving image signals are handled, a processing amount of compression processing for each moving image signal has to be controlled.
In International Publication No. 2006/033227, an proposal for the above-described problem has been raised. As illustrated in FIG. 14, a moving image encoding device 1400 that compression-encodes a plurality of moving image signals includes a signal number obtaining section 1410 that obtains the number of target moving image signals that correspond to input moving image signals in number and are to be encoded, a moving image obtaining section 1420 that obtains one or more of the target moving image signals that are to be encoded, a processing method specifying section 1430 that specifies a processing method for encoding processing which affects an arithmetic amount of the encoding processing, i.e., for example, a processing method regarding an upper limit of reference image frame number, and a motion vector search range, etc. in accordance with the number of moving image signals obtained by the signal number obtaining section 1410 such that as the number of the moving image signals increases, the arithmetic amount reduces, and an encoding section 1440 that performs encoding processing on the one or more moving image signals obtained by the moving image obtaining section 1420 and performs, if the number of the obtained moving image signals is plural, encoding processing on each of the obtained moving image signals on a time division basis. The encoding section 1440 is configured to perform encoding processing using a processing method specified by the processing method specifying section 1430.
In a motion prediction section 1442, motion prediction is performed in a search range sent from a motion prediction processing specifying section 1431. In this case, when the number of the moving image signals from the signal number obtaining section 1410 increases, the search range is limited to a small range.
In an intra encoding section 1443, intra prediction is performed in accordance with an intra prediction mode sent from an intra encoding processing method specifying section 1432. In this case, as the number of the moving image signals increases, the number of intra prediction modes is limited to a small number.
In a quantization section 1445, processing is executed by a quantization step sent from a quantization step size specifying section 1433. In this case, when the number of the moving image signals increases, the quantization step is limited to a small quantization step.
A variable-length encoding section 1446 operates in an encoding mode sent from a variable-length encoding processing specifying section 1434. In this case, when the number of the moving image signals increases, the variable-length encoding section 1446 operates in an encoding mode in which variable-length encoding is not performed.
As described above, when the number of the moving image signals increases, encoding processing is executed in a limited mode in order to reduce a processing amount of prediction processing (see, for example, International Publication No. 2006/033227).
These technologies are for use in recording devices, such as a digital versatile disc (DVD) or the like, which records programs of a plurality of television channels. In these technologies, the frame rates of handled input moving image signals are the same, a processing method that is to be used for a case in which there is no priority order for image qualities of the input moving image signals is adopted, and thus, the arithmetic amount of prediction processing for each of all moving image signals is disadvantageously reduced.